This invention relates generally to management techniques for a wireless communications network and, more particularly, to a system and method for determining frequency allocation in a multi-frequency wireless network.
There are many types of multiple-frequency mobile network technologies, including global systems mobile (xe2x80x9cGSMxe2x80x9d), time division multiple access (xe2x80x9cTDMAxe2x80x9d), and advanced mobile phone service (xe2x80x9cAMPSxe2x80x9d). Even common frequency technologies like code division multiple access (xe2x80x9cCDMAxe2x80x9d) often use multiple frequencies for linking different areas of telecommunication traffic. Likewise, there are many types of packet data technology that are being implemented with these mobile network technologies. For example, global packet radio services (xe2x80x9cGPRSxe2x80x9d) and enhanced data rate for GSM evolution (xe2x80x9cEDGExe2x80x9d) technologies are being developed to implement packet data technology for GSM and TDMA networks, respectively. For these technologies, it is important to utilize all the available bandwidth in order to maximize the efficient use of the network.
Consider for example a TDMA network where different frequency channels, referred to as simply xe2x80x9cfrequencies,xe2x80x9d are reused as often as possible for spectrum efficiency, but limited by the need to avoid interference and/or crosstalk. Simplistically, a most efficient use of frequencies would be similar to a map, where two adjacent cells never use the same xe2x80x9ccolorxe2x80x9d on the map. In real life, however, frequencies from one cell can often be xe2x80x9cseenxe2x80x9d even at non-adjacent cells. For example, several nonadjacent cells located in a valley-type land formation may not be able to use the same frequency because of the inherent physical characteristics of the valley, despite the fact that the cells are not adjacent or otherwise sufficiently separated. In another example, cells that are close but not adjacent in a downtown area with many tall buildings may allow frequent reuse of a frequency due to the blocking character of the tall buildings.
In furtherance of the TDMA network example, for a given cell, there is a certain radio frequency (xe2x80x9cRFxe2x80x9d) isolation limit (e.g. 17 dB) between a frequency in that cell and a frequency in another cell. Therefore, a particular frequency can be used in the given cell if that cell""s use of the frequency is 17 dB stronger than any residual use of the same frequency by another cell. If the frequencies are less than 17 dB apart, the caller will experience excessive interference or cross talk.
A simplistic solution to the frequency planning problem is to prepare fixed frequency plans for a predetermined number (a cluster) of cells. Common cluster sizes are seven or eleven cells, which are generic enough to work on a lot of different systems and different geographic layouts. The frequency reuse is scheduled for each cluster and then the cluster is repeated throughout the network.
A problem with the fixed frequency plans is that because they are generic to many different environments, they do not promote efficient frequency reuse. Also, there may be some environments that still experience significant crosstalk.
Referring to FIG. 1, a solution for the above identified problem is to generate an isolation matrix 6 for every cell or cell partition (which may be further divided into cell sectorsxe2x80x94hereinafter simply referred to as xe2x80x9ccellxe2x80x9d) in the network. The isolation matrix 6 specifies the frequency isolation of a cell from every other cell in the network. A demand matrix 7 can also be used to designate high-use cells (e.g., in downtown areas) from low-use cells (e.g., in rural areas). An automatic frequency planning system 8 may then take the isolation and demand matrices and determine the appropriate frequency plan among the cells in the network.
One way to populate the isolation matrix 6 is to set up a transmitter in one cell and then move around a test cell with a measuring device. Typically, a test vehicle is outfitted with a receiver and measuring device to roam around the test cell and obtain measurements. Once the test cell has been covered, the isolation between the two cells can be determined.
This solution has many problems. First of all, it is not uncommon that the test procedure has errors associated with manual or human intervention. Secondly, the test vehicle may not sufficiently cover the test cell. Thirdly, it is difficult and expensive to repeat this process in a large network to account for changes in the environment.
Therefore, it is desired to have a more accurate system and method for deriving an isolation matrix for a given network.
It is further desired to have a system that can be easily repeated to accommodate changes in a network""s environment.
It is still further desired to have a highly accurate isolation matrix that is not dependent on mechanical or human performance.
In response to the problems and needs described above, provided is a system and method for creation of an isolation matrix for automatic frequency planning in a wireless communications network. In one embodiment, the method automatically determines frequency isolation between a first and second cell of the wireless communication network. The method broadcasts a first frequency in the first cell and a second frequency in the second cell. A mobile unit operating in the first cell measures both the first and second frequencies and report the measurements to a computing center. In some embodiments, the mobile unit repeatedly measures and reports the first and second frequencies. The difference between the first and second frequency is computed and analyzed to determine the frequency isolation.
In some embodiments, the measurement difference(s) are stored in an isolation matrix for statistical analysis.
In some embodiments, the method is used with a plurality of mobile units, thereby increasing the number of provided measurements.
In some embodiments, the mobile unit may measure the strength of the first and second frequencies using a mobile assisted handoff method. The first frequency may be the actual carrier servicing the mobile unit""s call in the first cell. The mobile unit may then report the measurements using a channel quality message. A plurality of channel quality messages may be collected.
A benefit of the present invention is that it provides a more accurate system and method for deriving an isolation matrix for a given network.
Another benefit of the present invention is that it provides a system that can be easily repeated to accommodate changes in a network""s environment.
Yet another benefit of the present invention is that it provides an accurate isolation matrix that is not dependent on mechanical or human performance.
Yet another benefit of the present invention is that it relies on existing measurement mechanisms available in IS-136 TDMA and GSM cellular networks.
Yet another benefit of the present invention is that measurements are taken from actual calls serviced by each cell, therefore the portions of the cell""s coverage area included in the isolation matrix data is automatically representative of the traffic patterns of the cell.